LYNN — US Representative John F. Tierney and his Republican challenger, Richard R. Tisei, sparred Thursday over taxes and Washington gridlock in a surprisingly civil debate that was notable for what was never mentioned: how much Tierney might have known about the illegal gambling ring that was run by his wife’s brothers.

Controversy surrounding the gambling ring has made the race one of the most competitive and bitter in Massachusetts. A Republican political action committee that backs Tisei is running ads demanding that Tierney, an eight-term Salem Democrat, “man up and tell the truth — the whole truth,” about the gambling business.

But in their first debate, Tisei, a former state senator from Wakefield, did not mention the issue. Speaking to reporters after the debate, he said he wanted to respect the organizers at MassINC, a think tank, who wanted to keep a strict focus on jobs, the economy, and the middle class. Still, MassINC officials said the candidates were free to bring up any issue.

In a face-off that was more an exchange of quips than knockout blows, neither candidate appeared to sway a crowd of several hundred that seemed evenly divided among Tierney and Tisei supporters. Most of the debate, held at North Shore Community College, focused on which candidate would be able to work effectively in a highly polarized Congress.

Tisei blasted Tierney as a partisan Democrat who has been unwilling to reach across the aisle.

“For all people who are frustrated with Washington gridlock, I ask you: What will change if John Tierney is reelected?” Tisei said.

Tierney repeatedly underscored his main theme: that Tisei is backed by conservative “Young Guns” in the House and will vote to put “ideological extremists” such as Representative Eric Cantor into the leadership.

He mentioned several times that Tisei has called the Tea Party a “godsend” and has labeled the deep spending cuts and sweeping Medicare changes proposed in the budget of Representative Paul Ryan a “good start.”

“Unfortunately, my opponent has sided with that group, with the Young Guns,” Tierney said.

Daniel Fishman, a Libertarian, also participated in the debate. He called himself an “average guy” with “a voice that is neither Republican or Democrat, but of the people.” Though he was seated between Tierney and Tisei, he was mostly ignored by them.

Rebutting Tierney’s charges that he will empower conservative Republicans in the House, Tisei frequently cited Democratic policies he supports. He said he backed President Obama’s executive order that suspended deportations for young illegal immigrants. He praised Governor Deval Patrick for supporting community colleges. Tisei also promised to vote against Ryan’s budget and reported that, when he was in the state Legislature, he voted against Governor Mitt Romney 46 percent of the time.

“I have a record of being able to work with Democrats to get things done, and that’s exactly what we need in Washington right now,” Tisei said.

But Tierney said that many of the issues Tisei promises to advance — such as overhauling immigration — would be sidelined by House Republicans.

“If your first vote is to put the Young Guns in charge, there will be no comprehensive reform,” Tierney said.

The only time Tisei embraced the idea of working with the Republican majority was when discussing a General Electric plant in Lynn that is threatened by cuts in defense spending. Tisei said it would be helpful to have one Republican in the state’s House delegation who could meet directly with Speaker John Boehner and urge him to protect the plant.

The candidates’ sharpest disagreements centered on Medicare and taxes. Even though Tisei said he would vote against Ryan’s budget, Tierney accused Tisei of supporting Ryan’s plan to “voucherize” Medicare. Tisei argued that Tierney has already hurt Medicare by supporting Obama’s health care law, which calls for a $700 billion reduction in the growth of the program. Tisei called that reduction a “cut” in Medicare, a charge Tierney dismissed as the “biggest lie in the century.”

On taxes, both candidates adhered to party orthodoxy. Tierney said he wants to let the Bush tax cuts expire for the wealthy, while Tisei said he wants to extend them for all income levels.

Tisei said his number one priority would be to repeal the medical device tax, which he said is hurting firms in the district. Tisei said that even some Democrats, including Senate candidate Elizabeth Warren, support the elimination of that tax. But Tierney said industry agreed to the tax as part of Obama’s health care law.

The serious exchanges were broken by a “lightning round” in which the candidates were asked to give one-word answers. On the Occupy movement, Tierney said “awareness;” Fishman said “enlightening;” and Tisei said “fraudulent,” sparking cheers.

Asked for a middle-class hero, Tisei said “my mother;” Fishman said “Tim Wakefield;” and Tierney said “Roosevelt’s labor secretary,” Frances Perkins, the first woman to serve in a presidential Cabinet and a champion of the New Deal.

Prompted for one word on the Citizens United ruling that opened the door for unlimited political spending by corporations and unions, Tierney said “bad,” Tisei said “Um, I would probably say bad,” and Fishman said “misunderstood.”